Apparatus for roasting ore



Jan. 2, 1951 K. D. MOBEAN ,9

APPARATUS FOR ROASTING ORE Filed Oct. 28, 1947 4 Sheets-Sheet 1 KD. IV!Bea-n Inventor ATTORNEY K. D. M BEAN APPARATUS FOR ROASTING ORE Jan. 2,1951 4 Sheets-Sheet 2 Filed Oct. 28, 1947 M a 6 m M D V w n e V V W 1ATTORNEY Jan. 2, 1951 K. D. MOBEAN APPARATUS FOR ROASTING om:

Filed Oct. 28, 1947 4 Sheets-Sheet 3 K. D. MBeam l'Yl veYlToY ATTOB NEY4 Sheets-Sheet 4 Jan. 2, 1951 K. D. M B EAN APPARATUS'FOR ROASTING OREFiled Oct. 28, 1947 Inventor AT TO R NEY K. D. MBean nMMmuH n H PatentedJan. 2, 1951 2,536,952 APPARATUS FOR ROASTING our;

1 Kenneth D. McBean, Trail, British Columbia,

1 Canada, assignor to The Consolidated Mining and Smelting Company ofCanada, Limited,

Montreal, Quebec, Canada, a corporation of Canada Application Octoberas, 1947, Serial No. 782,618

4 Claims.

This invention relates to an apparatus for roasting ore and concentratesand is particularly directed to the roasting of mineral sulphides ingaseous suspension.

Methods and apparatus for roasting mineral sulphides in gaseoussuspension are well known and are in relatively wide spread use. Ingeneral, the methods involve blowing a mixture of finely divided, driedmineral sulphide ore or concentrate particles into the upper part of acombustion chamber maintained by the heat of the combustion of theparticles at a relatively high temperature, wherein the particles aredisseminated concurrently with the air blast through it for the exposureof the surfaces of each particle to the oxidizing action of the hotcombustion gases. The

conversion of the sulphides to oxides is effected by the combustion ofthe sulphur content of the charge supported by the air of the blast. Theroasting temperature and the time of retention of the particles in thecombustion zone are regulated in such a manner as to promote theoxidation of the charge without fusion or incipient fusion. The roastedmaterial settling at the bottom of the combustion chamber is removed forfurther processing and the gaseous products of combustion are exhaustedfrom the combustion chamber having ahigh concentration of sulphurdioxide. Such methods and apparatus are disclosed in 'U. S; Patent No.1,884,348 and No. 1,963,282.

In roasting mineral sulphide particles in gaseous suspension accordingto known methods and apparatus, the sulphide particles have been driedon drying hearths placed above the combustion chamber or in separatedrying apparatus outside the roasting furnace.

An important object of the present invention I is to provide an improvedapparatus for roasting mineral sulphides in gaseoussuspension wherebythe productive capacity of the roasting furnace is substantiallyincreased with a substantial decrease in'capital and operating costs.

A further important object of the invention is to provide an improvedroasting furnace which permits the arrangement of the apparatus asso-'ciated with the roasting furnace, such as the feed bins-fans,conduitsand conveyors, at a low level,

preferably adjacent to the floor level, which reduces the amount ofheavy supporting structural steel required, and centralizes adjacent tothat level the control of the process.

A- further important object is to provide a novel design of roastingfurnace which may be readily modified to increase the capacity of thefurnace. This may be accomplished by merely, extending the combustionchamber and burners upwardly without extensive dismantling andrearrangement of the furnace and associated parts.

An understanding of the manner in which the above and other objects ofthe invention are attained may be had from the following description,reference being made to the accompanying drawings in which:

Figure 1 is a plan view illustrating schematically a preferredarrangement of the furnace and associated apparatus;

Figure 2 is a plan view in section taken along the line 2-2 of Figure 6;

Figure 3 is a plan view in section taken along the line 33 of Fi ure 6;

Figure 4 is a plan view in section taken alon the line 44 of Figure 6;

Figure 5 is a plan view in section taken along 'the line 5--5 of Figure6;

ent invention;

Figure 7 is a side elevation illustrating a, preferred arrangement fordistributing dried ore particles to the burners; I

Figure 8 is a side elevation illustrating a preferred arrangement of theroasting furnace and associated storing and feeding apparatus; and

Figure 9 is a side elevation in section of the roasting furnaceillustrating a preferred arrangement of conduits from the roastingchamber to the drying hearth and from the drying hearth to the intake ofthe burner fan.

Like reference characters refer to like parts throughout thespecification and drawings.

A preferred embodiment of the invention is illustrated in Figures 1 to 9inclusive and comprises, in general, a roasting furnace indicated by thenumeral 20, a grinding mill 2|, such as a ball mill, for pulverizing theore to a high degree of.

fineness, a classifier 22 for classifying the pulverulent ore particlesfrom the grinding mill, and a blower 61 for distributing the oreparticles to the burners, and associated fans, conveyors, ducts andstorage bins, all of which are described in detail hereinafter.

The roasting furnace 20 is preferably a vertically disposed, elongatedcylindrical metal shell internally lined with heat insulating material30, such as refractory bricks, capable of withstanding the hightemperature corrosive and erosive actions of the gases and the particlesto which it is subjected. The outer surface of the shell is also coveredwith insulating material 3|, such as asbestos. to minimize heat lossesthrough the shell.

The upper part of the furnace is in the form or an elongated,unobstructed combustion chamber 32 closed at the top by a steel cover 33interhally lined with refractory heat-insulating material, and at thebottom by the uppermost collecting hearth 34. The combustion chamber isof a height sufficient to permit the substantially com plete oxidationof the particles as they fall to the uppermost collecting hearth 34 andof a diameter su'iilcient to permit the tho'rbugh dissemination of theparticles therein.

The collecting hearths 34 and 35 and the drying hearth 36 are positionedin the lower part of the furnace below the combustion chamber. Theuppermost collecting hearth slopes slightly upwardly from the shell ofthe furnace towards a centrally disposed shaft 31 to terminate short ofthe shaft to provide between the shaft and the rim of the hearth anannular drophole 36 leading to the lower hearth 35.

The lower hearth 35 is similar in construction to the upper hearth 34and extends downwardly from a point adjacent to the shaft 31 to theinner lining of the furnace shell. An outlet drophole 36 is provided inthe hearth 35 and extends through the furnace shell for the dischargefrom the furnace of roasted particles collected on the hearth 35.

The particles collected on the lower collecting hearth 35 are moved byrabbles 61 attached to rabble arms carried by the shaft towards theperiphery of the furnace and into the discharge outlet 39 which extendsto a storage bin (not shown).

The chamber formed between the upper collecting hearth 34 and the lowerhearth 35 is provided with an outlet 62 in the furnace wall for thecombustion gas. This outlet 32 is located at a convenient place oppositethe discharge outlet 39. The combustion gases are withdrawn throughoutlet 82 and preferably passed through a wasteheat boiler and cyclone(not shown).

The drying hearth 36 is positioned below the lower collecting hearth 35.The drying chamber 25 is defined by the underside of the lowercollecting hearth 35 and the top of the drying hearth 36 and is isolatedfrom the collecting hearths except for such minor leakage of gas as mayoccur through the small space between the shaft and the lower collectinghearth. Hot combustion gases are withdrawn from the combustion chamberthrough the conduit 44, Figure 9, and passed into the drying chamber 25.

The shaft 31 is in the form of a hollow rotatable steel shell externallycovered with refractory heat-insulating material. The shaft extends froma point below the furnace to terminate a short distance above theuppermost collecting hearth 34. Rabble arms 46, 4i and 42 are carried bythe shaft and extend radially outwardly from the shaft to move, onrotation of the shaft, over the collecting hearths 34 and 35 and thedrying hearth 36 respectively. The rabble arms are hollow and areadapted internally for cooling by a cooling medium, such as air, fedinto the lower end of the shaft 31 through conduit 84 connected to asource of air under pressure, such as for example, a compressor (notshown) and discharged through conduit 65. The rabble arms are thusmaintained at a temperature substantially below the normal operatingtemperature of the furnace. The shaft is rotated at a predetermined rateby means of a conventional driving mechanism 33, which may be a motorconnected through a speed reduction gear box 4 to a pinion driving aring gear mounted on the shaft below the furnace.

The associated parts of the roasting furnace for storing the moist ore,drying the ore, grinding the dried ore, delivering the finely comminuted, dried ore particles to the burners, and the circulation ofcombustion air and hot combustion gases are described hereinafter incon- Junction with the operation of the furnace and its associatedapparatus.

Moist sulphide ore particles are stored in the bin 50, and are fed,preferably at a predetermined rate, such as by a screw conveyor 5!, tothe periphery of the drying hearth 36.

The moist particles are advanced by the rabbles attached to the rabblearms 42, across the hearth 36 and during their passage across the hearth36 the particles are exposed to the hot combustion gases fed into thedrying chamber 25 from the combustion chamber 32 through the duct orconduit 44. The volume of the gas passing through the drying chamber 25may be regulated such as by a valve 66, so that substantially all themoisture is removed by the time the particles have travelled across thehearth 36. The particles are moved toward and into the drophole 52, andinto the conduit 53 which communicates with a conveyor 54. The conveyor54 advances the dried particles to the grinding mill 2!, such as a ballmill, wherein any agglomerations are broken up and any coarse particlesare ground to a finely comminuted state.

The dried, comminuted particles are carried from the grinding mill 2i inan air current generated by a fan or blower 26 through conduit 55,through the classifier 22 to a separator 56, such as a cycloneseparator, in which the air and the dried comminuted particles areseparated. The air on losing its burden of ore particles is returnedthrough conduit 51 by the blower 26 to the grinding mill 21. Any excessair from the grinding circuit is preferably fed from the blower 26through vent 53 to the burner fan inlet 16 to be used in the combustionof the sulphide particles.

The dried ore particles are arator 56 through a conduit storage bin 62,Figure 8. An 61 is provided in conduit 66.

The dried particles are fed at a predetermined rate by a conveyor 63positioned below the storage bin 62. The conveyor 63 advances the oreparticles to an air injector 64. The air injector 64 is connected to asource of high pressure air, such as a compressor (not shown) throughconduit 65. The ore particles are carried in the air blast to the burnercircuit.

The burner circuit preferably includes a conduit 66 connected at one endto a fan 61 and at the other end to a junction 66 at which the stream ofdried mineral sulphide particles and air is divided for distribution tothe burners. An opening in the conduit 66 is provided for the injectedstream of ore particles from the injector 64, as indicated by thenumeral 63. Excess air from the grinding circuit may be returned throughvent 53 to burner fan inlet 16.

Combustion gas is drawn through the drying chamber 25 and withdrawnthrough conduit 1| and returned through the burner fan inlet 13 to thecombustion chamber 32. Atmospheric air for supporting oxidation, orcombustion, of the sulphide particles is drawn into the burner cir-1cutit'ghrough the open end 12 of burner fan infed from the sep- 66 to adry feed air sealing valve The stream of combustion pended dried mineralsulphide particles is divided at junction 68, into substantially equalstreams for delivery to the burners l4 and 15,

each burner being supplied with approximately the same volume of themixture of gas and sulphide particles.

In the preferred modification of the invention, two diametricallyopposed burner nozzles 14 and 15 are extended angularly upwardly intothe upper part of the furnace. The burner nozzles l4 and 15 areconnected at their inlet ends to the conduits 16' and 11 respectivelywhich; in turn, are connected to the junction 68. To ensure propercombustion of the particles and to avoid the formation of accretions onthe furnace walls. the burner nozzles 14 and 15 are preferably gases andsusdirected angularly upwardly. If more than two burner nozzles are usedin the furnace, these are preferably spaced equidistantly around thecombustion chamber.

A scraper 80, carried by a stationary arm 8|, preferably in the form ofa water-cooledpipe, scrapes particles which have fallen on the top ofthe rotating shaft 31 and prevents their accumulation on the top of theshaft. I

The burner fan 61 forces a mixture of air and combustion gas into theconduit 66 for circulation to the burner nozzles 14 and 15. bustion gasis drawn from the combustion chamber through the conduit 44, and thedrying chamber 25, and from the drying chamber through the conduit II tothe burner inlet conduit 13 for Comnace. v

The embodiment of theinvention described in detail herein andillustrated in the drawings is capable of modification without departingfrom the scope of theinvention. For example,- in' 4 certain instances,it may be desired to discharge all or part of the gas from the dryingchamber to the atmosphere, or into the hot combustion gases passed tothe heat exchanger, or into the gases discharged :from the' heatexchanger,

rather than return it to the combustion chamber. Also, the gas from thedrying chamber may be passed through a-separator, such as a cycloneseparator for the removal of the entrained solids.

These entrained solids normally would include base of the furnace, therotating shaft is exadmixture with atmospheric air and is delivered tothe conduit 66 by fan 61. If desired, oxygen may be fed into the gassupplied to the burners to enrich the gas mixture. Additional air may besupplied to the burner circuit by by-passing air from the grindingcircuit through conduit 58.

Hot combustion gases are withdrawn from the furnace through the outlet82 in the furnace wall at a point adjacent to the periphery of the lowercollecting hearth. The hot combustion gases withdrawn from the furnaceare passed preferv ably through a heat exchanger, such as a wasteheatboiler, for the recovery of their heat value, and then passed through aseparator, such as a cyclone separator, for the removal of the entrainedsolids.

The design of the furnace and the arrangement of the associatedapparatus permit operation of the furnace to produce products of highquality at a highcapacity.

In operation, the dried mineral sulphide particles, on being blown intothe furnace, are rapidly dispersed in the hot combustion zone and,quickly reach their ignition temperature. The

roasted particles settle through the combustion chamber, on to theuppermost collecting hearth 34 whereon they are moved inwardly towardsand into the annular drophole 38 to fall on to the lower collectinghearth 35. The particles on hearth 35 are rabbled outwardly towards andinto conduit 39 through which they are removed from the furnace.

The rate of combustion and the temperature of the combustion chamber maybe closely controlled by varying the rate of feed of mineral sulphideparticles to the burner nozzles and the composition of the gaseoussuspension medium, which may be easily varied by increasing ordecreasing the rate of flow of atmospheric air or oxygen enriched air orcombustion gases from the drying chamber or by returning cooledcombustion gas from the exit of the heat exchanger.

tended only a short distance into the furnace leaving the combustionchamber free from any obstruction and thereby substantially increasingthe capacit of the furnace. This design of furnace has a furtherimportant advantage in that it permits the thorough dispersion of theparticles inthe hottest zone of the furnace to promote thoroughcombustion at a rapid rate and at the same time enables a relativelyhigh concentration of sulphur dioxide to be obtained in the exit gas anddiminishes the formation of zinc ferrates when the furnace is employedfor roasting zinc sulphides containing iron compounds.

Also, further increases in furnace capacity may be obtained by an easilyerected upward extension of the furnace and burners without majordismantling and reconstruction operations.

The design of the furnace makes possible the concentration of apparatusassociated with the furnace at or adjacent to the floor level withattendant substantial reduction in capital cost and important savings inoperating costs and facilitates close control over the operation of theapparatus.

What I claim as new and desire to protect by Letters Patent of theUnited States is:

1. In a furnace for roasting mineral sulphides in gaseous suspension, avertically elongated, unobstructed combustion chamber, an inlet fordried comminuted mineral sulphide particles in the upper part of saidchamber, at least one collecting hearth below said combustion chamber,an outlet for roasted ore particles and an outlet for hot combustiongases from the collecting hearth, at least one drying hearth below thecollectin hearth for drying the combustion chamber feed material,conduit means extending from the combustion chamber to a drying chamberdefined by the collecting hearth and the drying hearth, an inlet formoist sulphide particles to the drying hearth. an outlet for driedsulphide particles from The air or oxygen enriched air isintroduced withthe mineral. sulphide particles fed" to the burners l4 and 15 inthe'upper part of the-fur.- nace chamber. It is not necessary tointroducecombustion air or oxygen elsewhere in the= furthe dryinghearth, an outlet for gases from the drying chamber, means for conveyingdried sulphide particles from the drying chamber to the combustionchamber, a rotatable shaft extending from a point below the furnace toterminate a short distance above the uppermost collecting hearth, rabblearms carried by said shaft, and rabbles carried by said arms adapted tomove on said hearths.

2. In a furnace for roasting mineral sulphides in gaseous suspension, avertically elongated, unobstructed combustion chamber, means forinjecting a mixture of oxidizing gas and dried, comminuted mineralsulphide particles into the upper part of the combustion chamber, atleast one collecting hearth below said combustion chamber, an outlet forroasted ore particles and an outlet for hot combustion gases from thecollecting hearth, at least one drying hearth below the collectinghearth for drying the combustion chamber feed material, conduit meansextending from the combustion chamber to a drying chamber defined by thecollecting hearth and the drying hearth, an inlet for moist sulphideparticles to the drying hearth. an outlet for dried sulphide particlesfrom the drying hearth, an outlet for gases from the drying chamber,means for conveying dried sulphide particles from the drying chamber tothe combustion chamber, a hollow rotatable-shaft extending from a pointbelow the furnace to terminate above but adjacent to the uppermostcollecting hearth, rabble arms carried by said shaft, rabbles carried bysaid arms adapt-- ed to move on said hearths, and means for feeding acoolant through said shaft and rabble arms.

3. In a furnace for roasting mineral sulphides in gaseous suspension, avertically elongated, unobstructed combustion chamber, means for in-Jecting a mixture of oxidizing gas and comminuted mineral sulphideparticles into the upper part of the combustion chamber, at least onecollecting hearth below the combustion chamber, an outlet for roastedore particles and an outlet for hot combustion gases from the collectinghearth, at least one drying hearth below the collecting hearth fordrying the combustion chamber feed material, a drying chamber defined bythe collecting hearth and the drying hearth, means for feeding moistmineral sulphide particles to the drying hearth, conduit means extendingfrom the combustion chamber to the drying chamber, an outlet for driedsulphide particles from the drying hearth, means for conveying driedsulphide particles from the drying chamber to the 8 combustion chamber.conduit means for returning gas from the drying chamber to thecombustion chamber, a rotatable shaft extending from a point below thefurnace to terminate a short distance above the uppermost collectinghearth, rabble arms-carried by said shaft, and rabblu carried by saidarms adapted to move on said hearths.

4. In a furnace for roasting mineral sulphides in gaseous suspension, avertically elongated, unobstructed combustion chamber, means for in-Jecting a mixture of oxidizing gas and comminuted mineral sulphideparticles into the upper part of the combustion chamber, at least onecollecting hearth below the combustion chamber, an outlet for roastedore particles from the collecting hearth, a separate outlet for hotcombustion gases adjacent to the collecting hearth, a drying hearthbelow the collecting hearth, a drying chamber defined by the collectinghearth and the drying hearth, means for feeding moist sulphide oreparticles to the drying hearth, conduit means extending from thecombustion chamber to the drying chamber, an outlet from the dryinghearth for dried sulphide particles, means communicating with the lastmentioned outlet for pulverizing said dried sulphide particles, meansfor advancing the dried comminuted sulphide particles to the combustionchamber, and conduit means for mixing an oxidizing gas with gas from thedrying chamber'for admixture with the dried sulphide particles, arotatable shaft extending from a point below the furnace to terminate ashort distance above the uppermost collecting hearth.

, rabble arms carried by said shaft, and rabbles carried by said armsadapted to move on said hearths.

KENNETH D. McBEAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,929,308 Clarke Oct. 3, 19331,929,713 Queneau Oct. 10, 1933 1,963,282 Stimmel et a1. June 19, 19342,002,496 Freeman May 28, 1935 2,088,195 Ferguson July 2'7, 19372,104,091 Mullen Jan. 4, 1938 2,120,475 Stimmel et al. June 14, 19382,302,841 Connolly Nov. 24. 1942

1. IN A FURNACE FOR ROASTING MINERAL SULPHIDES IN GASEOUS SUSPENSION, AVERTICALLY ELONGATED, UNOBSTRUCTED COMBUSTION CHAMBER, AN INLET FORDRIED COMMINUTED MINERAL SULPHIDE PARTICLES IN THE UPPER PART OF SAIDCHAMBER, AT LEAST ONE COLLECTING HEARTH BELOW SAID COMBUSTION CHAMBER,AN OUTLET FOR ROASTED ORE PARTICLES AND AN OUTLET FOR HOT COMBUSTIONGASES FROM THE COLLECTING HEARTH, AT LEAST ONE DRYING HEARTH BELOW THECOLLECTING HEARTH FOR DRYING COMBUSTION CHAMBER FEED MATERIAL, CONDUITMEANS EXTENDING FROM THE COMBUSTION CHAMBER TO A DRYING CHAMBER DEFINEDBY THE COLLECTING HEARTH AND THE DRYING HEARTH, AN INLET FOR MOISTSULPHIDE PARTICLES TO THE DRYING HEARTH, AN OUTLET FOR DRIED SULPHIDEPARTICLES FROM THE DRYING HEARTH, AN OUTLET FOR GASES FROM THE DRYINGCHAMBER, MEANS FOR CONVEYING DRIED SULPHIDE PARTICLES FROM THE DRYINGCHAMBER TO THE COMBUSTION CHAMBER, A ROTATABLE SHAFT EXTENDING FROM APOINT BELOW THE FURNACE TO TERMINATE A SHORT DISTANCE ABOVE THEUPPERMOST COLLECTING HEARTH, RABBLE ARMS CARRIED BY SAID SHAFT, ANDRABBLES CARIED BY SAID ARMS ADAPTED TO MOVE ON SAID HEARTHS.